The present invention relates to a process for working up the hydrogen fluoride phase of reaction mixtures from fluorination reactions.
Fluorine-containing hydrocarbons are produced on a large scale by reacting halogenated hydrocarbons with hydrogen fluoride. Usually one starts with chlorine-containing hydrocarbons. In addition to fully halogenated carbon compounds, compounds which also contain hydrogen in addition to fluorine (and optionally chlorine) may of course also be used or produced. Alkenes may for instance also be used as starting materials for the preparation of fluorine-containing hydrocarbons, so that hydrogen fluoride addition also takes place. Compounds of this type have become important as replacements for fully halogenated carbon compounds.
A process of this type is described in published German Patent Application No. DE 4,005,945. Ethane derivatives containing trifluoromethyl groups, such as CF.sub.3 CHCl.sub.2, are prepared from halogen-containing alkenes or alkanes, with a halogen-fluorine exchange and optionally addition of hydrogen fluoride. In the course of working-up the reaction mixture, volatile reaction products are first collected in a phase separator. In so doing, two separate phases are obtained. The heavy phase contains predominantly organic compounds, in particular the desired reaction product. The lighter phase contains predominantly hydrogen fluoride and water. The hydrogen fluoride phase is recycled to the fluorination reaction. Any readily volatile constituents released in the phase separator are passed through a gas scrubber. The disadvantage of this process is that the water contained in the hydrogen fluoride phase is recycled.